Triethyl tin (TET) is an organo metal representative of a class of chemicals that produce vacuolization and splitting of myelin. To date, there has been a limited amount of work reported concerning the effects of TET on developing organisms. The following research concerns the effects of TET given during the postnatal phase of development of the rat. The purpose of the research is to: (1) attempt to identify dose related changes in behavioral functioning of rats when tested at different times after exposure (days 21-190 of age), (2) attempt to determine any long-term effects on neurotransmitter binding, and (3) attempt to assess the functional significance of any observed neurobehavioral and neurochemical effects using special psychopharmacological procedures.